Polyplexes of plasmid with synthetic polycationic vectors, such as linear polyethylenimine (LPEI), have been widely investigated. While much is known about the role of physicochemical characterization of the polycation in transfection, the role of serum components in the transfection using LPEI-polyplexes needs further investigation. In this study, bovine serum albumin was incorporated into the polyplex, either through precomplexation with circular DNA coding for green fluorescent protein prior to polyplex formation with LPEI or after formation of the polyplex. The transfection efficiency of these ternary polyplexes was then studied in He La cells. It was observed that the order of incorporation of albumin into polyplexes has a distinct effect on its uptake and transfection efficiency. Through colocalization and albumin depletion studies, we conclude that albumin plays a role in both the translocation of the complex into the cell and its unpackaging.